There are a number of automatic and semi-automatic rifles used by military personnel as well as law enforcement and civilians. While fully automatic rifles are generally illegal for use by the civilian population, many of the components which constitute an automatic rifle are the same as those found within semi-automatic models legalized for civilian use. Arguably the most popular semi-automatic assault-type rifle used by civilians, particularly within the United States, is the AR-15 and its clones. AR-15 is a registered trademark of Colt Industries. A number of additional companies manufacture clones of the AR-15 and market these clones under separate trademarks. While used throughout the specification, it is to be understood that the term AR-15 is meant to include not only those rifles manufactured by Colt Industries, but also those additional clones and any variants thereof. The AR-15 is the semi-automatic variant of the fully automatic M16 rifle used by United States military personnel.
The AR-15 and M16 are designed as modular rifles generally comprising a buttstock, lower receiver, upper receiver and barrel assembly. Each component is separable from one another and affords rifle owners the opportunity to customize the rifle with after-market components such as barrels of differing lengths, upper receivers designed to handle different calibers of ammunition, flashlights, hand guards, grenade or flare launchers, flash or sound suppressors, grips, and front or rear sights. To operate, the lower receiver is configured to include a trigger and magazine box wherein activation of the trigger causes a round (bullet) housed within the chamber of the upper receiver to be fired out the barrel of the rifle by action of a reciprocating bolt carrier group housed within the upper receiver. Internal mechanisms of the upper receiver expel the shell casing of the fired round from the chamber while components engaged with the magazine box housed within the lower receiver feed a new round into the now-empty chamber. The buttstock mounts to the lower receiver and includes a buffer assembly and action (or recoil) spring in communication with the bolt carrier group. After a spent shell has been discharged, the spring urges the bolt carrier group back toward the chamber in preparation for firing another round.
The modular construction of these rifles enables generally quick and easy field-stripping (disassembly of the rifle for cleaning of the rifle to ensure proper firing of the weapon). In field-stripping the rifle, the lower receiver is separated from the upper receiver to gain access to the firing mechanism (bolt, bolt carrier and associated mechanisms) for cleaning and re-lubrication. When assembled, the upper and lower receivers are secured to one another through rear and forward extensions on the upper receiver fitting between corresponding sidewalls forming notches or grooves on the lower receiver. The forward sidewalls and extension are fitted with a pivot pin to prevent the forward halves of the receivers from separating. Similarly, the rear sidewalls and extension employ a takedown pin to secure the two receivers together. To field-strip the rifle, the takedown pin is sufficiently pushed out of the extension so as to enable the rear extension to lift out of the rear sidewalls thereby pivoting the lower and upper receivers about the pivot pin. The pivot pin can then be pushed out a sufficient distance so as to enable removal of the front extension from the front sidewalls and thereby completing separation of the lower receiver from the upper receiver.
While the AR-15 and M16 can be constructed of aircraft grade forged aluminum, a trend in manufacturing current firearms/firearm components is to interchange metal parts/components with high strength polymeric materials, such as glass reinforced nylon, whenever possible. These polymeric parts/components decrease the weight of the rifle while also decreasing material costs associated with fabrication of the rifle or individual rifle parts. One drawback in polymeric components, however, is the eventual wear of these components after repeated field-stripping, cleaning and reassembly. This is of particular importance with regard to the upper and lower receivers and the takedown and pivot pins. Any substantial wear to any of the components results in an unsafe and unusable firearm. A further drawback to a polymeric upper receiver is the potential for fatigue or cracking of the upper receiver through repeated impacts upon the polymer by the reciprocating bolt carrier group.
Further, typical rifle systems employ a gas tube running from the forward sight post on the barrel to the chamber within the upper receiver. Hot gas is generated during the firing of a round. A portion of this hot gas enters the gas tube where it travels back to the chamber. Hot gas entering the chamber forces the bolt and bolt carrier rearward against the buffer spring and leads to extraction and ejection of the spent round. The buffer spring then propels the bolt and carrier forward where another round is loaded from the magazine. The repeated exposure to hot gas may lead to melting, brittling or other premature failure of a polymeric upper receiver.
Still further, polymeric upper receivers may fail due to flexing or bowing of the receiver, particularly the top portions thereof. The upper receiver must be a generally hollow structure so as to house the bolt carrier group and form the chamber. As a result, the upper receiver is generally constructed as a thin walled member. Part of the appeal of the modular rifle, and particularly the AR-15, is that the rifle can be modified/customized with after-market accessories as described above. However, these accessories weigh on the rails which are formed along the top surface of upper receiver. This additional weight can lead to flexing or bowing of the thin-walled polymer, thereby leading to an unsafe or inoperable rifle.
As such, there is a need for an upper receiver assembly which capitalizes upon the weight and cost savings afforded by polymeric materials while also enjoying the mechanical and structural strength afforded by metal (i.e. aircraft grade aluminum). The present invention addresses these and other needs.